Organic EL devices are known to be highly efficient and are capable of producing a wide range of colors. Useful applications such as flat-panel displays have been contemplated. The work on the improvement in organic EL devices such as color, stability, efficiency and fabrication methods have been disclosed in U.S. Pat. Nos: 4,356,429; 4,539,507; 4,720,432; 4,885,211; 5,151,629; 5,150,006; 5,141,671; 5,073,446; 5,061,569; 5,059,862; 5,059,861; 5,047,687; 4,950,950; 4,769,292, 5,104,740; 5,227,252; 5,256,945; 5,069,975; 5,122,711; 5,366,811; 5,126,214; 5,142,343; 5,389,444; 5,458,977; 5,536,949; and 5,683,823.
The organic EL device includes an organic EL element consisting of extremely thin layers (&lt;1.0 micrometer in combined thickness) between the anode and the cathode. Herein, the organic EL element is defined as the organic composition between the anode and cathode electrodes. In a basic two-layer EL device structure, one organic layer of the EL element adjacent to the anode is specifically chosen to inject and transport holes, therefore, it is referred to as the hole transport layer, and the other organic layer is specifically chosen to inject and transport electrons, referred to as the electron transport layer. The interface between the two layers provides an efficient site for the recombination of the injected hole-electron pair and the resultant electroluminescence. There is also a three layer organic EL device which contains a light-emitting layer between the hole transport layer and electron transport layer that has been disclosed by Tang et al [J. Applied Physics, Vol. 65, Pages 3610-3616, 1989]. The light-emitting layer commonly consists of a host material doped with a guest material. The host materials in light-emitting layer can be electron transport materials, such as 8-hydroxyquinoline aluminum complex [U.S. Pat. No. 4,769,292], the hole transport materials, such as aryl amines [Y. Hamada, T. Sano, K. Shibata and K. Kuroki, Jpn. J. Appl. Phys. 34, 824,1995], or the charge injection auxiliary materials, such as stilbene derivatives [C. Hosokawa et al., Appl. Phys. Lett., 67(25) 3853, 1995]. The doped guest materials, also known as the dopant, is usually chosen from highly fluorescent dyes. In the three layer organic EL device, the light-emitting layer provides an efficient site for the recombination of the injected hole-electron pair followed by the energy transfer to the guest material and produces the highly efficient electroluminescence.
In general, the host material in the light emitting layer should be as fluorescent as possible and the fluorescence wavelength should be in the blue or near the UV region. The latter attribute is important for down-shifting of the EL emission wavelength in a host-guest emitter layer. Among the blue fluorescent materials, 9,10-(diphenyl)anthracene has a near unity fluorescence quantum efficiency in solution. This compound is also highly fluorescent in the solid state. However, as a host material for the EL emitter layer, the film-forming property of 9,10-(diphenyl)anthracene is very poor, resulting in highly polycrystalline film which tends to produce electrical shorts in the EL device. Several improvements in 9,10-(diphenyl)anthracene have been disclosed. EP 0681019 disclosed the use of a dimeric structure of 9,10-(diphenyl)anthracene in improving the film-forming property and the solid fluorescence efficiency. EP 0786926 disclosed that the amino derivatives of 9,10-(diphenyl)anthracene are useful as emitters in organic EL device.